If a dye may run, soak the garment for an hour in 1/2 gallon of water to which you've added 1/2 cup vinegar and 1/2 cup salt. If rinse water shows color, repeat. This is good for a single-colored fabric or madras. If the item is multicolored, dry-clean it. (American-made fabrics are unlikely to run, but fabrics from abroad are sometimes risky.)